This invention relates to a system for accurately positioning and locating a workpiece between the centers of a machine tool, and further to such a system, employed at the headstock spindle of the machine tool, which permits rapid accommodation of workpieces of various size having center holes of various diameters.
Generally, before a workpiece can be machined in a machine tool, a center hole must be drilled at each end of the workpiece so that the workpiece can be supported by the centers of the machine tool. This drilling operation is usually performed on a lathe or on a special center-drilling machine. The diameter of the center drill is determined primarily by the size of the piece to be machined: i.e., a workpiece of a large diameter would require a larger center drill than one of small diameter, since the former would need stronger support between centers. When a series of workpieces or parts to be machined are center-drilled, the depth of the center hole at the headstock end of the workpiece is normally kept approximately the same for all parts, so that once the machine has been set up for one part, additional parts can be machined without changing the initial set-up. However, a problem arises because the very act of drilling the center hole has proven not to be sufficiently accurate for many applications. Since the depths of the center-drilled holes can vary by a considerable amount, serious machining problems can arise. For example, if one wished to grind a number of shafts to incorporate a flange at a certain distance from the end of the shaft, it would be time-consuming and costly to reset the grinding tool for each piece in order to compensate for the differing depths of the center holes and the resulting relative change of position of the workpiece.
One solution to this problem is afforded by a procedure which involves the internal lapping and depth inspection of each individual workpiece, using an abrasive paste lapping compound. Although effective, the center-hole lapping method is extremely time-consuming and very expensive.
Another attempted solution is disclosed in U.S. Pat. No. 979,034 to Rowe et al., which concerns a device mounted in the live spindle of a lathe, having a center with a stop or shoulder against which the workpiece may be positioned. The center includes a spring-mounted center pin which projects beyond the shoulder or stop, and which center pin is adapted to recede to permit the workpiece to be carried against the shoulder when placed in position in the machine. In this way, compensation is made for any variation in the center hole depth of a series of workpieces without the necessity for re-setting the tool for each piece. However, the Rowe et al. device suffers from several shortcomings. For example, each Rowe et al. device is limited to use of a center pin of a single size, and no provision is made for quick and economical change of the center in order to accept workpieces of various sizes having center holes of widely differing diameters, without the need to replace the entire device in the machine. Furthermore, Rowe et al. does not make provision for securing the center pin in place once the workpiece is positioned thereon. Nor does Rowe et al permit use of the device to machine a workpiece of diameter smaller than that of its center pin.
It is therefore an object of this invention to provide an improved center stop system that will permit rapid interchangeability of centers of various size so as to accommodate workpieces having center holes of variously sized diameters. It is a further object of this invention to permit such interchangeability without the necessity of replacing the entire center stop device in the machine. It is a still further object of this invention to provide an improved device that will permit securing the spring-mounted center pin in a given position after the workpiece is positioned thereon. And it is another object of this invention to permit convenient utilization of the system with a workpiece of diameter less than that of the center pin.
Objects and advantages of the invention are set forth in part above and in part below. In addition, these and other objects and advantages of the invention will become apparent herefrom, or may be appreciated by practice with the invention, the same being realized and attained by the instrumentalities, combinations, and methodologies pointed out in the appended claims. Accordingly, the invention resides in the novel parts, arrangements, combinations, steps, methods, and improvements herein shown and described.